The present invention relates to a duty control circuit used to change gradually the duty factor, e.g. the ratio of OFF period to ON period for the current supplied to a lamp, thereby dimming the lamp gradually.
In recent years, centralized control for automobiles has become more and more advanced. In controlling the ON-OFF of a courtesy or interior lamp as one of the controls for automobiles, the courtesy lamp is sometimes required to dim gradually when it is turned off by a timer some time after a certain switch has been turned off. But, no suitable digital integrated circuit meeting such a requirement has been available.